The present invention relates to a vacuum variable capacitor for various circuits such as an oscillating circuit of a super power oscillator, an RF power circuit, and a tank circuit of an induction heating apparatus, and more particularly, to the vacuum variable capacitor with energization and heat shielding bellows.
Vacuum capacitors are broadly divided into a vacuum fixed capacitor wherein a capacitance value is fixed and a vacuum variable capacitor wherein a capacitance value can be varied.
The characteristics required of the vacuum variable capacitor are lower power loss, less heat generation during energization, longer life, etc. As will be described hereinafter in detail, the vacuum variable capacitor comprises an adjustment screw, the temperature of which becomes very high (up to about 300° C. by estimate) due to convection/radiation from the air side of a bellows as a heat generation source and heat conduction from the bellows, electrodes, center pin as heat generation sources through a movable-electrode support plate and a movable lead. A reduction in internal heat generation of the vacuum variable capacitor and in conduction of this generated heat to the adjustment screw is an important factor involved in increasing the life of the vacuum variable capacitor.